1. Field of the Invention.
The present invention relates to a device for making an accurate measurement of deformation of a specimen when a jacket to contain the specimen is required.
2. Description of the Prior Art.
Properties of rock and other mineral materials may be determined in controlled laboratory tests. Typically in these tests, a representative specimen of the material is loaded by a testing apparatus. During the test, measurement of the load upon the specimen and measurement of the deformation of the specimen under load are required to characterize the mechanical behavior of the material. To provide accurate measurement of the deformation of the specimen, deformation measurement devices (extensometers) are mounted directly on the specimen under test. Extensometers should directly engage the specimen surface, but usually mineral specimens are jacketed. If the extensometers are mounted on the outer surface of the jacket, the deformation measurement will include a component of deformation contributed by the specimen and also a component of deformation contributed by compression of the jacket.
The mechanical behavior, such as the compression strength of many materials depends on the pressure surrounding the specimen. To simulate such pressure, the specimens are placed inside pressure vessels during test. A space between the specimen and the pressure vessel wall is filled with a fluid which can be pressurized and which may also serve to uniformly heat the specimen. Because of the presence of this pressurizing fluid, the specimen needs to be jacketed to prevent the fluid from contacting the specimen and/or physically or chemically reacting with the specimen.
There are several loading frames for testing the mechanical properties of material. Two such devices are disclosed in Barnaby U.S. Pat. No. 4,562,726, and Heuer, Jr. et al. U.S. Pat. No. 3,199,341, which test for the compressibility of specimens. The disclosures of these two patents show jackets made of a flexible material, but neither shows any sort of contact between a measurement device and the jacket.
Two other prior patents, Lutenegger et al. U.S. Pat. No. 4,122,704 and Handy et al. U.S. Pat. No. 4,047,425, disclose testing devices for measuring lateral expansion induced in a specimen by applying an axial compressive load. The devices shown in these two patents use a cylindrical specimen housing with a slit in the wall of the cylinder. A measuring device is associated with this slit to provide a measurement of lateral expansion. However, neither of these devices includes a flexible jacket around the specimen nor a measurement device making direct contact with such a flexible jacket.
Bishop et al. U.S. Pat. No. 3,505,860 discloses a test apparatus with a fluid pressurized chamber for varying the pressure of the specimen while it is tested. The specimen is contained within a flexible material jacket, but the apparatus does not include an extensometer mounted in direct contact with the material covering the specimen. A similar apparatus is shown in Strom U.S. Pat. No. 3,616,685. Brower et al. U.S. Pat. No. 4,599,891 discloses an apparatus to hold a material specimen.
None of the test systems use a measurement device (extensometer) with a jacketed specimen, where the effects of compressibility of the jacket are eliminated.